There are many applications where it is desirable and/or necessary to trace or locate the position of a concealed conductive element, such as an underground cable or pipe. Prior art techniques have been proposed in the past for coupling an electrical signal to the conductive element at a frequency so as to produce remotely detectable radiation. A portable receiver, which is tuned to the particular electrical signal's frequency, is then passed over the area and conventional signal detection techniques are used to pinpoint the location and path of the conductive element. Unfortunately, these prior art techniques are not capable of locating or identifying any covert surveillance devices that may be coupled to the line under test. Also, these prior art techniques are not capable of locating or identifying other types of non-linear junctions such as produced by corrosive metals, or dissimilar metals that may be of interest for specific applications. Therefore, what is needed is an improved line tracing method and apparatus that locates and identifies non-linear junctions coupled to a transmission line.
Non-linear junction detectors, such as described in U.S. Pat. Nos. 6,057,765 and 6,163,259 which are assigned to the assignee of the present invention and hereby incorporated in the present application by reference, for detecting the presence of concealed electronic devices are known in the prior art. However, these detectors are not capable of locating and tracing conductive transmission lines concealed within the walls of a structure. Thus, prior art non-linear junction detectors must be methodically scanned over an entire area to locate any concealed surveillance devices. Furthermore, these detectors are incapable of determining whether a located semiconductor device is coupled to a transmission line or not. Therefore, what is needed is a non-linear junction detector that can trace transmission lines and identify any electronics coupled to the line being traced.